text:
Which are the requirements to fly a N-registered aircraft operated by a non-US airline?
There are several non-US airlines which operate N-registered aircraft for domestic and international flights.
Let's say for instance Avianca, which has N-registered aircraft but is a non-US airline (flag carrier of Colombia with headquarters in Bogotá and main hub at El Dorado International Airport). What are the pilot certificates required to fly those aircraft? FAA or Colombian pilot certificates?

Related; it's the opposite of this question

The flights could be branded Avianca but operated by a 3rd party.

Some operator use wet leased aircraft in order to be allowed to fly in EU.

There are a few aspects to this. First off all N-Registered aircraft must be owned and operated by a US based entity. As has been mentioned this could be any US based company or US resident. In reality foreign companies can set up US based branches or entities fairly easily under which to own the aircraft. The aircraft must also comply with all FAA regulations for maintaining the N-Number (annual inspections etc.) This means that the aircraft must be inspected at an FAA approved/licensed facility (they do exist outside the US). The planes can (if practical) be flown back into the US for inspections if no foreign facility is available.
When it comes to flying the plane the pilot must carry what ever is locally required to fly in and out of that country/airspace both from an equipment standpoint and a pilot standpoint. Many countries will accept/recognize different pilots certificates for inbound international traffic, that is the subject of its own question as there are many combinations out there. For what its worth the US FAA certificate and the ICAO/EASA certificate are pretty highly recognized around the world.

"locally required" as it is written in the text can be confusing and misinterpreted : it doesn't matter where you fly  (in any of the ICAO countries). What you need is a licence issued (or accepted) by the authority that registered the plane. That is you need FAA licence to operate N-registered aircraft (anywhere in the world). No question about it. Similarly, I can operate a YR- (Romanian registered) plane in and out of U.S. ONLY with a Romanian issued licence. Operating YR- a/c in Mexico with FAA licence is not allowed,etc


text:
What does this handle from the movie Flight (2012) do?
I wanted to ask about something that, as an aviation enthusiast I have never seen before, from the movie Flight with Denzel Washington. Perhaps the reason is is because it's a movie.

You pull these up, turn them clockwise, and push them back down. Something about "reverting manual control". I have never seen anything like those handles in a jet cockpit before.
The handle is used in a scene in this YouTube video (blocked in many countries, alternative video, also blocked) between 2:34 and 3:40.

If you search under "reverting to manual controls" as mentioned in the script, you may find enough information to answer your question.  Otherwise I'm sure someone here will recognize the aircraft type and offer a good answer on the context of what's happening in this scene.

Comment not an answer because I'm not a pilot... but I'm almost certain those "revert to manual control" handles are not part of real jets. The autopilot disconnect switch is just that, a switch—usually button switch and usually on the center console. Not a big mechanically-linked handle.

@randomhead The Autopilot disconnect is on the yoke where a pilot with 1 hand on the yoke & 1 on the throttles can reach it immediately. Turning off the A/P on the center Mode Control Panel (same switch/button that engages it) will work too.  I'll defer to a DC-9 pilot on that handle, but like you I suspect it's movie dramatics... on a Boeing, manual reversion simply happens when the hydraulic pressure is gone. There's a switch you turn on to get a standby pump powering the rudder, but you have aileron/elevators immediately. That movie got so much so wildly wrong, this detail too, probably.

Movies do get a lot wrong, and I've never flown a plane with this exact system, but I have enough experience that it's believable that an older plane with hydraulically boosted controls would have a large T handle to mechanically disconnect a failed system and revert to an emergency backup mode.  Hoping someone here will validate that opinion with a credible answer...

The lever is what's known as a 'plot device'.

The movie Flight (2012) shows a McDonnell Douglas MD-80 series aircraft (same as Alaska Airlines Flight 261, on which it is loosely based). There is no such handle in an MD-80 cockpit. Compare the following scene from the movie (left) with a photo of a real MD-80 cockpit aft pedestal (right):

(left: cropped from YouTube video, right: modified from hilmerby.com)
In the movie, the captain says

We gotta revert to manual control

This does not make sense for an MD-80 because ailerons and elevator are always under manual control (only the rudder is hydraulically powered with manual reversion):

Lateral Control System
Control column wheels are used for lateral control. Control wheels are cable
connected to an aileron control tab and are linked together by a torque tube
arrangement that causes both control wheels to move together. [...]
Aerodynamic forces on the control tabs move the ailerons. [...]
Longitudinal Control System
The longitudinal control system is a pair of elevators attached to the
horizontal stabilizer. The elevator control is, for all normal flying, an
aerodynamic boost system that operates a single control tab on each elevator.
Each control tab is driven by an independent two-way cable system from the
corresponding control column in the cockpit.

(MD-80 Flight Manual - Section 11 Flight Controls)
There is a hydraulic boost system for the elevator, but that is only active during high angle-of-attack situations:

A 3000 psi hydraulic power augmentor system provides elevator control for
additional nosedown capability in extreme, high angle-of-attack flight
conditions.

(MD-80 Flight Manual - Section 11 Flight Controls)
By the way, the real accident was caused by a failure in the trimmable horizontal stabilizer (THS) assembly (and the THS is powered electrically, not hydraulically; you can see the stabilizer trim primary motor brake switch under the red cover in the right photo above):

The National Transportation Safety Board determines that the probable cause of
this accident was a loss of airplane pitch control resulting from the in-flight failure of the
horizontal stabilizer trim system jackscrew assembly's acme nut threads. The thread
failure was caused by excessive wear resulting from Alaska Airlines' insufficient
lubrication of the jackscrew assembly.

(NTSB final report for ASA261 3.2 Probable Cause)

Wow. Just as I thought. Completely made up. Thank you for such a detailed answer with references to manuals and the NTSB report for Alaska 261. Well done.

I watched the clip and was glad I didn't go see the movie because I would've been screaming in the theatre will all the made up nonsense and ridiculous procedural depictions (no crew acts like that), and eventually walked out. Just infuriating, because the public comes away thinking that's how things are done.
You should assume ANY technical detail you see in a movie is the made up imaginings of a screen writer, except with rare exceptions, like Apollo 13. There almost certainly would have been a debate between the screen writer and the technical consultant on the movie, who would've been similarly ranting about the technical details, but procedural and technical realism might have taken the edge off the drama so the producer would go with the screen writer.
In the real world, a T-handle in an airliner cockpit will most likely be for one of 3 things:

To disconnect left and right control systems for pitch or roll control in case of a mechanical system jam in a conventional system with control cable circuits. They will be pull and turn to lock, and normally located up on the center console somewhere in prominent spots, releasing a lock that allows each side of a torque tube below the cockpit floor, that joins the left and right elevator or aileron control systems, to move independently.
To operate an hydraulic dump valve for the landing gear for emergency extension.  Pull and turn to open the hydraulic circuit to the gear actuators so the actuators can't impede the gears' freefall down.
Parking brake.  Pull and turn to lock, sometimes while holding the brake pedals forward, to lock the brakes on.

A handle that is not painted with a red/white or black/yellow barber pole pattern with prominent labelling, like the one in the picture, I would assume is a parking brake, although I would make sure before I tried to use it.
When the copilot pulls the T handle on the right side, in a normal world that would have been pulling a pitch disconnect to allow the left and right elevators to move independently, which is what you do with an elevator jam or runwaway. Unfortunately the dialog is total gibberish.
So treat all movies, except those that went to specific lengths to depict things accurately, as "science fiction", and temporarily suspend disbelief. Good idea to extend this to all films depicting any technical topic, like, say, nuclear power.  And news reporting, while you're at it...

Ars you a pilot? This is also an outstanding answer. I'd mark them both as answers if I could. Thank you.

Thanks, Yes I learned to fly in 1975, ex bush pilot, have a type rating on CRJs, and was a tech support engineering specialist for many years on the CRJ program.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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text:
Regarding 49 CFR 830, what is considered an in-flight fire?
49 CFR 830.5 requires immediate notification for in-flight fires.
Does that mean there must have been visible plasma?  Would the presence of smoke alone be enough to report that there was a fire, or would something that simply smolders not meet the standard of an in-flight fire?

No, there does not need to be visible plasma, and smoke alone is enough to constitute a fire onboard an aircraft.
FAA Advisory Circular 120-80A contains the following definitions that indicate that a visible flame is not the only definition meaning "fire" pertaining to aircraft.  In my experience, it's reasonable to expect that the FAA's definitions in this case would fall in line with the NTSB's definitions.
Hidden Fires:

Fires that are “hidden” are not readily accessible, may be difficult
  to locate, and are more challenging to extinguish. Some examples of
  hidden fires would be fires behind sidewall paneling or in overhead
  areas.

Smoldering Fire:

Combustion without a visible flame and a slow combustion rate are
  characteristics of a smoldering fire. A smoldering fire left
  unattended or an incompletely extinguished fire can ignite and grow
  into a larger, uncontrollable fire in a short time.

Suppressed Fire:

A fire that has been partially extinguished which may or may not have
  visible flames. A suppressed fire, if not extinguished, may
  reestablish itself and grow into a larger, uncontrollable fire in a
  short period of time.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Do airline pilots have to wear face masks in the cockpit because of COVID?
Do the flight crew with a commercial airline have to wear a face mask while on the flight deck, as both crew are in close proximity to each other and in a tight confined area? If not, why not?

Interesting article here:  https://www.paddleyourownkanoo.com/2020/10/07/american-airlines-pilots-removed-from-flights-for-asking-colleagues-to-wear-a-face-mask/

It probably depends which airline you're talking about.
At mine, we're given the choice. I choose not to wear it once the cockpit door is closed. I'd rather have clearer ATC communications, clearer intracockpit communications, and a better chance of successfully donning my oxygen mask in time to prevent incapacitation if it becomes necessary. The immediate safety of all of the people on the airplane is more important to me than the very marginal benefit a mask would provide to my own health.

Does flying 'mask free' also aid the 2 pilots with interpreting each other's 'body language' too ?

I can answer this question accurately - not as an airline pilot directly, but as the son of two.
To keep it short, no. Airline pilots are free to make their own decision about their safety in the cockpit. In the airport, yes. In the taxi, bus, or ground transportation, yes. But, when they enter the cockpit, they usually sanitize the entire touch area, use some germ-x, and settle in for the 12-14 hour flight. When going back into the cabin, they put a mask back on (while on break).
There have been some cases reported in the pilot body but not enough to cause any large issue. Thanks for your question.

This certainly feels like the right answer, but do we know that no airlines have mandated the wearing of masks. This answer is essentially a single data point - your parent's airline has not mandated it

I am also aware from them that the same practice is occurring at the other major airlines in the United States.

This YouTube video also confirms the same practice for a major European airline.

I'd like to add to this answer that there may be flight safety concerns with the use of masks. In an emergency like a pressure drop, face masks may prevent the pilot(s) from putting on their oxygen masks in time or add additional workload to an already hectic situation. They could interfere with talking clearly to the other pilot or ATC, or be moved up and down by jaw movement that may seem trivial, but may be disturbing if a dangerous flight situation were to happen suddenly

I am not answering because the common use of "airline" is large part 121 jets with cockpit doors.  However, I fly part time for a small airline and our policy is to wear masks.  But this is flying a Cessna Caravan, with no barrier between crew and passengers...  FWIW.


text:
Rotor Tip Speed vs Forward Airspeed - IAS or TAS?

I created this graph to illustrate how the tip speed of the advancing and retreating blades vary with forward airspeed but am confused as to what would be the most correct way to label the x-axis:

IAS
TAS
it doesn't matter
it depends on the application

NB: Graph is based on the following data:

The y-axis is a derivative of the x-axis: $$y= 672 ± \frac{6076x}{3600}$$
eg: At $x = 100KTS$, $$y=672±169 FPS$$
  From POH: rotor RPM @ 100% = 510RPM = 672FPS @ 151 inch rotor diameter

It depends. What are you using the graph for?

Maybe I should add a it depends option in my question. I guess ultimately the different tip speeds are only meaningful because of dissymmetry of lift, in which case the answer to my question is TAS because that's what's used to calculate lift. On the other hand, I don't think that if it was labelled IAS that would be wrong either, would it? Is there any other reason to care about differing tip speeds?

At a given angle of attack, lift is proportional to IAS, not TAS. But TAS is proportional to Mach number (at fixed temperature), which is important for the advancing blade (should stay below Mach 1).

For this graph, only TAS can be correct.
More precisely, you should have the same kind of speed on both axes. Otherwise, you would need to qualify the altitude.
Your tip speed (the vertical axis) is (presumably) the simple geometric speed, which depends only on RPM. Or in other words, TAS (with no wind). It will have simple and universal linear relationship with forward TAS. But with IAS, it will be valid only at a certain altitude.
This could be both IAS, but I don't think helicopters just increase their rotor RPM with altitude the way airplanes increase TAS. This could be true for very slow rotors, but the real ones seem to be Mach-limited, so IAS is just not very useful. But correct me if I'm wrong.

Airplanes stall at the same indicated airspeed, not true airspeed.

Yes, but how is it relevant?

@Zeus Re: "More precisely, you should have the same kind of speed on both axes. I have updated my question to include how I created the graph (both axes use the same figures, I've just converted units). You have made me reflect to realise that linear velocity (eg:FPM) is about distance over time, and the analog of distance in the air would be TAS not IAS. To the best of my knowledge, most helicopters (if not all) use constant rotor RPM. Can you provide your rationale for "Only TAS can be correct"?

Well, that's exactly my rationale: if your tip speed velocity is derived from [constant] RPM, so you should use a 'compatible' linear speed, i.e. TAS. As you see, the tips vary the speed by ±169 fps of TAS (at 100 kt). You can't just add TAS to IAS, despite them having the same units. (BTW can't help but notice it would me much clearer in the metric system). Imagine the craft flies forward at 672 fps TAS: then the retarding blade stops. If it was 672 fps IAS, you couldn't conclude that: depending on altitude, the retarding blade would likely have some negative airspeed.


text:
Can an aircraft on loan in the US be based outside the US?
I'm interested if there is any possible way to get an aircraft (Piper Navajo Chieftain) on loan for a US citizen and then base the aircraft outside the USA?

If I understand you correctly, you want to loan an aircraft in the US and then base it outside of the US? I updated the question accordingly. If you wanted to know something else, please edit again to clarify.

Yes, you understand correctly.....

Any US-registered aircraft can be based in any country subject to that country's rules. Just check with your local aviation authorities in the country where you want the aircraft to be based before you reposition the aircraft. Some may require you to depart the country every so many days/weeks/months, sometimes in as simple a way as a short hop across a border, but to my knowledge most don't have any restrictions.

Just make sure it’s allowed by the loan agreement and insurance!

I don't think the OP is talking about a financial loan, but yes, insurance covering it would be a good idea. Insurance doesn't allow or disallow as it can't stop you from doing things that are not covered. It just means you are on your own.

I get it, just offering a little unsolicited business/legal advice.  Because while the FAA may not care, Avemco or the owner sure might.

AVEMCO has no say whatsoever on where an aircraft can be operated, only on when they will pay a claim.

Kinda my point…

Consider as well that there is no law against having multiple insurance coverages for anything. You can have a policy that covers an aircraft operating in the US, and have a different one that only covers the aircraft while operating in EMEA because the coverage is cheaper for that region of the world.


text:
Why does each fan blade have a different mass and frequency?
From a documentary (at 16:39) on building a Rolls-Royce jet engine:

... no two finished blades are exactly alike, and with twenty in each fan, it will only spin smoothly if the blades are perfectly balanced, so every one is precisely measured and weighed then rung like a bell. Each blade has a different mass and different frequency ...

Is it hard to develop blades of identical mass, or are there other reasons for the different masses and frequencies?

"despite the precision of the engineering, no two finished blades are exactly alike"

Because manufacturing processes are not perfect, and the minute differences between parts as-designed and as-produced are amplified by the high rotational speeds and large diameters of modern jet engines.
Take a following back-of-the-envelope calculation: disregard incoming airflow velocity and assume a hypothetical fan with a 1 meter diameter rotates at such rpm that the blade tip has a tangential velocity of 80% of the speed of sound at 35kft in ISA. The equivalent rpm would be 2817.
$$
a_c=\frac{v^2}{r}=\frac{(295\cdot0.8)^2}{1}=55.7\cdot10^3 \; \mathrm{[m/s^2]}
$$
That's the acceleration on the blade tip. If this blade were to be just 1 gram overweight, the force exerted on it would be:
$$
F_c=m\cdot a_c=0.001 \cdot 55.7\cdot10^3=55.7 \; \mathrm{[N]}
$$
that force is more than the weight of a 5kg dumbbell and it alternates its direction almost 3000 times per minute.
Its not that fan blades are hard to manufacture precisely, but that the application in which they are used is unusually demanding and any small imperfection in the blade will make itself known very loudly.

As for why the frequency is different, it is because the vibration modes of any system depend on the spatial mass distribution, like a pendulum which changes its natural frequency if you shorten the distance between the mass and the fulcrum. So the two issues you mention are directly related: a few milligrams of metal missing at the tip will shift the center of mass, and with it the natural frequencies of the blade.
In reality the whole vibration issue is a bit more complicated for continuous bodies, which effectively have infinite natural frequencies, because unlike ideal pendulums, their mass is distributed over infinite points in space, but that is a bit beyond the current point.
The important part is not to have any natural frequency coincide with the rotational frequency of the fan, because that would quickly lead to rapid unplanned disassembly: the vibration amplitude would be amplified with each revolution until the blade failed.

Very well written and a nice illustrative example! I'd love to add the keywords "resonance" or "eigenfrequency" to your last point, as you can find a lot of examples when searching for these.

I deliberately avoided speaking about eigenvalues because the question was quite simple and I wanted to keep the language accessible, but yeah, maybe it can be revised. I'll have a look when I get home.

I understand your point, and I agree, you certainly don't have to use them in your explanation - I thought however, that it would help people find other occurences of the same phenomenon, maybe just as some pointers.

"...rapid unplanned disassembly". That made me laugh. As for using mathematical terms like eigenvalues, perhaps you could edit your post to leave the bulk of it in layman's terms but add something like ("If you want to learn more on the topic, you can search on terms like 'resonance frequnency' and 'eigenvalue'.")

"... force ...  alternates its direction ..." We are talking about centrifugal force here, right? Why would it alternate its direction?

@Vlad You need to not think about the turbine like a spinning disk, and instead think of the centre of the turbine as an Olympic hammer thrower, and the blade as the hammer. Centrifugal force (actually centripetal force, but that's a separate conversation) acts down the blade. The force down the blade does not change, but the blade itself rotates. If the blades aren't perfectly balanced, the rotor shaft will pull in the direction of the heaviest blade(s), and that force rotates with the blades.

@DuncanC "That made me laugh." RUD (U can be unplanned or unscheduled) is a common enough tongue-in-cheek term used in rocketry, where RUDs are a way of life.

When I was a kid I got ahold of some black powder and put it in the parachute section of a model rocket, leading to a Rapid Planned Disassembly. Nowadays doing that would get me a long stretch in the pokey, but the statute of limitations has long since passed.

"Its not that fan blades are hard to manufacture precisely". That is true of some blades, but actually the carbon fiber composite ones like GE uses are fairly hard to manufacture.  Many composite parts require manual processes.  Before the resin is added and cured, the carbon fiber is a basically a flimsy fabric sheet.  Robots are good at manipulating rigid things, but flexible fabric is tricky.  So many steps are done by hand, leading to manufacturing variability between blades.

"The important part is not to have any natural frequency coincide with the rotational frequency of the fan" - doesn't the rotational frequency change as the fan spins up and then as power is adjusted? Is what you mean that the natural frequency needs to be more than the top rotational frequency of the fan?

So the G force that blades are subjet to is 5000 G ? shocking.

@AEhere supports Monica Would you mind writing maths as what flawr mentioned i.e eigen values with the blades or should i ask separate question?

@Auberron I'll add a paragraph when able, but there is enough in this topic for a multiple additional questions, so if you want to ask something specific, go ahead.

@AEhere supports Monica Thanks for your response.

There are advantages in the blades not being "perfectly identical". If all the vibration frequencies were exactly the same, when the blades were assembled to make the complete fan the vibrations would be coupled together and the blades could resonate with a large amplitude, causing increased noise and potentially reducing the life of the blades because of the increased oscillating stresses.
The blades are arranged in a pattern which minimizes not only the amount of unbalance, but also any "regular patterns" in the different vibration frequencies. For example if there are 20 blades in the fan, you don't want every fourth blade or every fifth blade to have close frequencies since these form regular repeating patterns.
Computer software is used to create the "best" arrangement of blades to meet all the criteria. For a fan with 20 blades this might not seem such a huge problem to solve, but some stages in the turbine may have more than 100 blades around a single disk.
The measurement of the blade frequencies when new is also important for safety checks later.If any internal cracks start to develop frequencies will change, and this is a useful way to check for damage as a supplement to X-raying the blades, etc. In some engines the vibration frequencies are "measured" continuously from the vibrations of the engine while it is running, and a change in the frequency spectrum gives an early warning of problems developing.

So if a blade has to be replaced, does the entire disc have to be re-balanced, possibly including changing other blades?

@AndrewMorton yes - if any blade is replaced the unit will need rebalancing. How could it not ?

From the number of nasty fan (and to a lesser extent, compressor and turbine) failures in recent history, it sounds to me like like engine designers may have gone a little too far in reaching for performance. That, or airlines are just getting sloppy in their maintenance procedures...

@PhilPerry are you sure you have evidence that failure rates are higher than they used to be?

ETOPS ratings suggest engines as a whole are becoming more reliable every decade.

@PhilPerry or there are lots more airplanes and lots more engines, so a rare event can happen more often, and catch your attention. That and selection bias - you probably don’t remember all the engine failures from 10 years ago.


text:
Cockpit vs Flight Deck?
Is there a distinction between a cockpit and a flight deck on an aircraft, or are the terms interchangeable?
Boeing refers to the flight deck The new Flight-Deck Displays and Airbus refers to the cockpit Passenger Aircraft>Cockpits
Based on this image,

would the B-2 be described as having a cockpit or a flight deck, or is there not enough information in this image?

Well if you ask an FO, it's a flight deck untill the captain steps in...

They refer to the same thing, but there is some separation between the terms, especially in the military. A cockpit is a hole with a seat that you strap into for the entire flight. A flight deck is a larger version of a cockpit, where you can at least leave your seat and walk behind it.
The traditional nautical term "cockpit" referred to a fairly small steering station at the top of the ship. Boeing introduced the term "Flight deck" post-WWII for their larger aircraft, to indicate the difference, and it has spread somewhat. A heavy's flight deck is still a cockpit, and can be referred to as such, but a "pointy's" (jet fighter) cockpit is very unlikely to be called a flight deck in speech.
In general and civil aviation, the terms are pretty much interchangeable. Still, a Ultralight Aircraft's cockpit is not a flight deck, so there is a strong connotation of a flight deck actually being a deck.
The B-2 has a flight deck, so do some fighters like the Su-34. Both can be called a cockpit as well. Basically, solo or tandem seating with entry through the canopy = "cockpit". Side-by-side seating with side door or bottom hatch entry = either "flight deck" or "cockpit".
This distinction is largely English-specific. Powered flight was being concurrently developed in France and Russia, and many languages ended up following their convention ("Piloting post/cabin" and "Crew cabin" respectively), where no term distinction was ever created.

I assume the term pointy refers an aircraft with a very narrow area where the pilot sits and cannot get up and move around.  Technically wouldn't the images from both Airbus and Boeing be of flight decks?

@Bob516 Pointy = jet fighter (because of their pointy noses). I deliberately used jargon, because this is very much an English-specific jargon/terminology question.

Flight decks are cockpits, much like squares are rectangles. The inverse is not true.

"Cockpit" was the cockfights arena. Used to refer to a lower deck portion on a military ship where wounded people were looked after (attested as far as 1706 in French language). This place was allocated to young officers when not needed otherwise. For civil boats, the place for the helmsman and the crew (1878). Later (1887) used to refer to the bottom place in a small boat where people could seat. In 1915, used in aviation for the open sky place where pilot (s) could be seated. Pit refers to the bottom, deck is "above" (closing the hull of a ship).

Congratulations on this answer making it into the official Congressional Report on the crashes of the 737 MAX!  (it's on page 8)

@SteveV. Thanks, never noticed!

New link to the report: https://s3.documentcloud.org/documents/7209479/2020-09-15-FINAL-737-MAX-Report-for-Public-Release.pdf

The terms are one in the same.  Cockpit is a little more archaic and derives from a nautical term used by the Royal Navy.  But both terms mean the section of an aircraft where the flight crew is stationed in order to command and control the flight of that aircraft.

Of interest: https://www.quora.com/Why-is-a-cockpit-called-a-cockpit. Note the reference to the term "cockpit"  originally referring to a below-deck compartment in a ship (is this really accurate?), and also the reference to the term "flight deck" orginating with flying boats. Another answer suggests the use of the  "cockpit" term in the nautical context goes all the way back to the Middle Ages and is a connected with the term "coxwain".
Here's another source emphasizing the original below-deck connotation for the nautical use of "cockpit":  http://www.aerospaceweb.org/question/history/q0064.shtml
Obviously, in the aviation context, "cockpit" is the older term.
"Flight deck" has a connotation of some amount of open space, while "cockpit" has a connotation of a confined space.  The usage of both terms has expanded beyond these connotations, but more so for "cockpit" than for "flight deck".
It seems intuitive that to merit the term "flight deck", at least one and usually  all of the following should be true:

During flight, you can walk to the area from another part of the plane
You can move about the area in flight to some extent (change seats, stand up, something.)
There is well-defined, mostly flat floor throughout a good portion of the area.

"the term "cockpit" originally referring to a below-deck compartment in a ship (is this really accurate?)" I think so, and not only in English. I posted a general comment below the accepted answer.

Some organizations prefer one term in their style guide, while others prefer the other. There is no substantive difference between them that I've ever encountered.


text:
What are the unique shapes of the weapons control switches in a F-14?
In his answer to the question Muscle memory for weapons systems? Michael Hall mentioned "'blind fold cockpit checks'... (learning to) locate certain switches by feel, reinforcing muscle memory to both locate them and identify them by their often unique shape."
These illustrations of F-14 control panels

F-14 weapons control panels, and

F-14 control panel
show the switchology (hey, I learned a new word) of the aircraft.
I don't see any distinct differences in the shapes in these diagrams.  What at the different shapes used in an F-14 to distinguish switches by feel?  Are there any other clues to help in the assistance of locating by feel?
If information about the shapes of switches (or other means to identify by feel) in other combat aircraft is available as an alternative, that would suffice to answer my question.

This question covers civilian aircraft, but it's related

I think your question needs to be more specific.  First, whose military are you asking about?  I can't imagine that a MiG-25 would have much in common with an F-14, or a British Harrier or whatever the French are making these days.  And second, is there even commonality between aircraft of one country?  Is the F-35 the same as the F-14 or F-16?


text:
Is there a typical time on site during an investigation of a major accident?
An answer to the question Why does it take months, sometimes years, for the BEA and NTSB to complete aviation accident investigations? said,

Visiting the Site - First there will be a team that heads to the incident site to collect information. If the site is easily accessible, this may be a fairly quick process. If the site is tough to access, or takes a while to find, this will of course take much longer. This is generally the part most visible to the public, but is only the tip of the iceberg in generating a useful report.

When the site is easily accessible, what is the typical (or average) amount of time spent on site collecting data of a major accident?

I think this really depends... for a small airplane crash this could be a few hours or a day, for a major accident this could be weeks.

@RonBeyer When you say weeks, do you mean two or three, or six to eight?  Not looking for a definitive answer, just a general idea of the length of time.

Again, it depends. For a relatively contained accident this may be 2-3 weeks, for something more distributed it may be longer.

Even when accessible, "the site" may be an extremely large area (e.g. D-AIPX), and critical element debris difficult to find for a team of 50 persons.

There are simply too many variables to answer this question, even in general terms.  And wreckage accessibility is just a small part of it.
If an aircraft runs off the end of the runway and the pilot survives to make a statement that can be corroborated by another crewmember, tower and other eyewitnesses, as well as weather reports, it doesn't take much time to wrap things up.  Probably a few days is all that is actually needed on-site.  Most of the work at that point is administrative in writing the report.  The aircraft may even be mostly intact and towable.
However, when all you have is a smoking hole in the middle of a pasture, as accessible as the wreckage may, be the investigator's workload is massive.  Sifting through all the broken pieces, numbering and cataloging them, plotting locations in the debris field, etc. can take months in itself, and then the real investigation begins.  Not to mention the cleanup.

"Sifting through all the broken pieces, numbering and cataloging them, plotting locations in the debris field, etc. can take months in itself" And if the farmer who owns the property goes "Sure, but I've got a schedule to keep for planting, so you get it out of here by X date or I'm going to drive my tractor through it"?

Farmer John is well compensated to leave his tractor in the barn.


text:
Typesetting aircraft manuals in the typewriter era
I'm trying to make sense of the table of limitations for the Viper 301 engine. This is from the Dominie T Mk.1 Ground Handling Notes I was fortunate to photograph at Kew a few years back.

The typist has written something like:
Condition         Rev/min per cent
----------------------------------
Ground idling     40 + 10
                     -  0

Does this mean "40% to 50% RPM" essentially? If so, why not "45 ± 5" - the same typist has written ± elsewhere in the same document.
Or does it mean the idling RPM will generally be 40% and might sometimes rise to no more than 50%?
(Yes, I realise I'm quite definitely overthinking this. I'm also wondering how many times this poor typist had to write lb/sq. in. in their career before PSI became an accepted abbreviation...)
edit: ah, this is the reason I doubted my initial assumption - a few pages later the typist has written this:

which I think means 40-41% N1 in modern terms? But they've written 12 - 25 lb/sq. in. just above... so confused.

You're going to be lucky to find anyone who really can answer authoritatively.  But doesn't it make sense that if the target is 40%, with 10% greater ok but anything under 40% not ok, that that's a different concept from what you suggested?

The typewriter/old era isn't important, because it's used in engineering today. A 0 tolerance on one side is called a unilateral tolerance, a range that is different between each side is a unequal bilateral tolerance.

This is not a typesetting thing, all of these different notations have a different meaning.
$ x\pm y $ means that the nominal ideal value is $x$, and up to $y$ deviation is acceptable.
$ x^{+y}_{-0} $ means that the nominal ideal value is $x$, and up to $y$ deviation is acceptable in the upward direction only. No deviation in the downward direction is acceptable. An example of a modern usage of this is in the instrument PTS:

Maintains the MDA, when reached, within +100 feet, −0 feet
to the MAP.

When flying a non-precision approach, the ideal is to fly exactly to the MDA and remain there. Upward deviations of up to 100 feet are allowed, but going below by even a foot is a failure.
A range $x–y$ states that any value between $x$ and $y$ is acceptable, without specifying any specific value as better than others.


text:
Can the 787 mini navigation display be controlled independently from the ND?
Some aircraft, e.g., the Boeing 787 have the option to display a "Mini Navigation Display" on the left Outboard Display Unit, right under the Primary Flight Display:

(image source)
Is the information shown there a copy of the "normal" Navigation Display on the Inboard Display Unit (possibly with a limited set of information?), or can it be fully customized by the pilot independently of the other ND? (I'm not talking differences between left and right side PFDs/NDs, but I'm talking only one side, e.g. the left side only).
With "copy of normal ND" I specifically mean ALL updates to the ND via the EFIS control panel are reflected on both the ND and the mini ND. This would include wx, airports, range, modes (plan, arc, rose), etc.
In case of independent controls, how can the pilot customize the mini ND?

The MiniMap is not an option, it's there as standard.
It's fixed at 20-miles range; the optional items are Wxr, Terrain and Traffic. The classic STA, WPT and ARPT from the ND are not available.
The MiniMap shows ADF needles, whereas the ND shows VOR needles.
The MiniMap looks like a development of the previous compass-rose at the bottom of the PFD, but it's mostly of little practical benefit. The major use of the MiniMap is to show Terrain while having Wxr on the ND, a dual-view that wasn't possible before.

so does that mean that the mini ND is not customizable beyond Wx, Terrain, Traffic?

Do you know how to turn on the Terrain and Weather Radar at the same time? I only see one set of buttons (WXR, TFC, TERR) on the glareshield.

I don’t know of any airplane where you can have Wxr and Terrain on the same screen at the same time. The system used to display the Terrain is the same as the Wxr - in effect the Terrain display is a created Wxr display. The nice thing on the 787 is the VSD (the profile view of the flight) which shows the terrain versus the pink string - much nicer than the MiniMap.


text:
Are Light Sport Aircraft: Certified, Experimental or a third separate category?
Is a Light Sport aircraft considered to be A certified or experimental aircraft? or is Light Sport a completely different third category?

Usually these are lumped into experimental LSAs and special LSAs. Are you asking about the latter?

About both I guess. A friend is telling me that LSAs are not certified or experimental, they are a distinct, third category that does not overlap.

I mean, by definition it’s pretty easy to figure out what category experimental LSAs fit in.

Perhaps what might clear up my confusion on this is seeing the non-overlapping list of "categorys" that all aircraft must be one of. You know, like the 50 U.S. states. Any geographic point in the US must be located in one and only one state. Aren't FAA "categories" like that? What are the "categories"?

I mean if the comment "pretty easy to figure out what category experimental LSAs fit in." implies that that "LSA"  is itself Not a category, if it "fits in" to some actual FAA defined aircraft "category". Are all these terms just horribly and mess-ily overloaded?

Light Sport is not Experimental, (which includes amateur homebuilt aircraft, warbirds, etc.) it is a category of its own within the broader group of Certified aircraft.
So it's not really a "completely different third category", but more of a different set of standards that exists within Certified.

You are commingling certification and category. All aircraft in the US are certified by the FAA (the FAA does not consider Ultralights to be aircraft). LSA, a category of small aircraft defined by the FAA using criteria such as maximum weight, number of seats, etc., are certified by the FAA under FAR 21.190 https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-21/subpart-H/section-21.190, as are Experimental aircraft https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-21/subpart-H/section-21.191. Experimental airworthiness certifications are issued irrespective of aircraft category, weight, number of seats, etc. I’m assuming you mean operating Experimental- Amateur Built aircraft when you state “experimental” as there are several other purposes experimental certifications are issued. A way to differentiate the certification process between Light Sport and Experimental is the FAA approval requirement for the aircraft manufacturer’s data, and the aircraft owner’s responsibility to adhere to the approved data. For example, for the LSA manufacturer to obtain a certification, the FAA must approve the LSA manufacturer’s Pilot Operating Handbook and Maintenance Procedures. The person that buys and/or pilots that aircraft must operate the aircraft in compliance with the approved data and may not arbitrarily substitute parts, alter, or repair a component without using the original manufacturer’s approved data.  These restrictions are not required of the manufacturer or any owner/operator of an aircraft certified as Experimental Amateur Built.


text:
How does static port measures the static pressure?
I have always thought that there is a probe or sensor kind of thing inside the static port so that it "measures" the static pressure and compare to other pressure sources for airspeed, altitude, and VSI reading.
But my other pilot friend recently told me that the way static port works is because of the air actually flows in and out of it.
For example, when you climb, the ambient pressure decreases so the air will flow out of the static port until it reaches equilibrium, which causes the static pressure inside the casing of altimeter to decrease and the altimeter shows an increase in altitude.
Tried to find answers about how static port work online but did not find a satisfying explanation...
If anyone knows more on this topic please share your opinion.

Your friend is correct. It's situated in a spot where the dynamic pressure is non-existent or minimal such as on the rear side of the fuselage on a Cessna 172 where it's able to measure the ambient pressure. This pressure is then either fed by tubes to their respective instruments (ASI, Altimeter, and VSI), or on modern aircraft, it is read by a transducer (or analog to to digital interface units - A/DIFU) which converts the reading to electronic data which is then fed to the air data computer.

Thanks for the replies! But this brings up another question of mine... how about pitot tube? I am sure that the air flows into the pitot tube but does it goes out of the tube as well? If it does, where is the exit? If it doesn't, isn't the ram air pressure going to keep accumulating inside the tube?

I don't think so. The pitot tube is designed to measure that ram air pressure (static + dynamic pressure) so it wouldn't make sense to drain it. It would only flow out if you slowed down.

There’s not a whole lot to a static port on an aircraft, though it is located at a point chosen where the boundary layer is at or very, very close to, the ambient air pressure.  The port opens to a static line which connects to the pilot static instrument or air data computers and this, along with the ram air (stagnation) pressure provided by the pilot tubes allows these instruments to calculate airspeeds, altitude and rates of climb or descent.

Static ports and pitot tubes do not measure anything. They are just holes with tubes leading to the interior of the aircraft. Instruments do the measuring.

Air will flow in and out of both static-port and pitot-tubes - you have to take all internal volume into consideration (mainly lines, instruments): As long is the "outside"  pressure (static and/or dynamic) is greater than the internal one, air will flow in, compressing (and doing the work inside the instruments) until both pressures are equal - than flow stops. When external pressure is lower - air will flow out until it is once again balanced. But this happens quite fast so in normal operation you can consider these ports closely linked to the instruments and disregard any flow.

Your friend is right.  There is no sensor inside a static port.  It is just a little tube connecting the static system (meaning all the tubing connected to altimeter, and the vertical speed indicator, and the static side of the airspeed indicator), to the outside.

Thanks for the replies! But this brings up another question of mine... how about pitot tube?I am sure that the air flows into the pitot tube but does it goes out of the tube as well? If it does, where is the exit? If it doesn't, isn't the ram air pressure going to keep accumulating inside the tube?

The pitot tube works similar to the static port except that its opening is in the free airflow. Meaning: The air does not flow through the pitot tube but rather into the opening and therefore creates an increased pressure inside the tube which is equivalent to the static pressure + dynamic pressure. Therefore, if the airplane slows down, the dynamic pressure decreases and air is flowing out of the pitot tube to the front until the pressure inside the tube is equivalent to static pressure + dynamic pressure again.


text:
What makes the Air Force and Navy pilots different?
As far as I know, aviation in both divisions are almost the same. They fly various aircrafts, they do dogfights, air to ground attacks, air transports, electronic attacks, and more. Can you say that Air Force and Navy pilots are different in some ways?

VTC as too broad. I could list some differences in the procedures they use, but this is such an open question I doubt we could run out of minor things to add to such a list.

One is called a pilot, the other an aviator

One flies back to the same place, t'other flies back to the same place in a different location. If that doesn't work, one walks back, t'other swims back.

Naval Aviators are generally more handsome than their USAF brethren, and we don't sing when we get drunk.

I don't know, but I understand that one group sport wings of lead, the other wings of gold.

Navel aviation pilots are specifically trained for anti ship and anti submarine warfare roles and they are also trained for carrier based operations. They are also trained for ground attack, dogfight etc. Air Force pilots does not have carrier based landing skills and they do not have anti submarine warfare capabilities.

Factually wrong, as multiple air forces worldwide have had antisubmarine aircraft grouped under the airforce rather than the navy, even when the navy had aviation assets as well.

Naval pilots. Navel pilots are something completely different


text:
how to know about designed airways above my house
Newbie here.
I hear quite a lot airplanes and helicopters and all kind of weird flying things above my head, at least one every 2 or 3 minutes, so I started tracking them with ADS-B.
There's a commercial airport in the region (MXP), not extremely close, but it seems that my house sits on some kind of airway (? not sure about the correct word) because everything leaving and approaching that airport to/from east just passes over my head making a lot of noise and I do not notice the same thing when driving nearby.
So my question is: is there a publicly available information about these routes? Are they static? I tried to check skyvector but I can't understand those.
Is there some kind of altitude limitation flights must comply? Just for fun, I'd like to compare those with ADS-B received data.
Edit: screenshot attached, on the left there's the airport, on the right two planes and an helicopter that just passed above my head.
Highlighted one is almost above my house.

Do you by any chance live directly north or south of the airport?

I am actually almost east, but the planes takeoff in north direction, then they turn back, let's see if I can attach a screenshot

When the wind is from the north airplanes will take off towards the north, if their destination is to the south or east they will be vectored in that direction.

Airways is a term that is used for the sort of "highways in the sky" that a lot of commercial air traffic use.
However, as you are reasonably close to an airport what you're most likely referring to is SIDS (Standard instrument departures) or STARS (Standard terminal arrivals). Both of these can be found quite easily by searching for the airport name/identifier along with those 2 terms
One such example is here: https://v1aviation.co.uk/wp-content/uploads/2016/10/LIMC.pdf
It is a long document with a lot of information, however around page 19 you start to see some example departure routes from one of the northerly runways, which do indeed turn east and west depending on the route the aircraft is taking. You might recognise some of the local topography and be able to estimate where your house is based on local knowledge.
Edited to add: The screenshot you have added looks similar to the easterly departure from 35L.

However, as pointed out in comments, the actual departure of that flight was from 35R, so the SID followed is likely to be the one later on in the linked PDF (pp 23-onwards).

Really interesting!
Is there in these maps also something related to altitude?

@vitom The underlined numbers on that SID are the not below altitudes at each point.

I disagree that the procedure shown in the screenshot of the answer is the same as the one in the question. the flight took off from 35R https://www.flightradar24.com/data/flights/az1019#21296241
the procedure followed is at page 20/23 of the pdf, through MC602/MC607

@Federico thanks, answer updated. I shouldn't have been so sure without checking the flight details.

np. personally I would change the image, but I leave the decision to you.

@Jamiec For altitudes on a SID/STAR, a line below means "not below", a line above means "not above", and both means "exactly".

@StephenS thanks. That was somewhere in the depths of my memory. But I wasnt 100% sure.

@StephenS even more interesting! I assume these are feet? I rarely see a plane above 4000m after the turn, in either 17R / 35R paths

@vitom Yes, aviation uses nautical units (feet, knots, etc.) unless otherwise specified.


text:
What does the AHRS do in the Garmin 175 series?
What function does the AHRS perform in the Garmin 175 series? And how long should it take to perform the initialization of the AHRS component in the initial system configuration process?

I am just installing a Garmin GPS 175, and everything seems to be working except that the AHRS Calibrate process in the configuration never seems to complete. I have tried it several times, once for about twenty minutes, and it never completes or provides any error messages, and the only way to terminate it is to power off the unit.

When in doubt, take a look at the manual for the unit

AHRS units have a magnetometer interface for determining magnetic heading.

The data may also be sent to any connected device like an iPad running foreflight.

(Source)

Duh!  Oh yeah, just read the manual, why didn't ....     - I  did read the users manual, and the installation manual, and the ARINC-429 interface specifications, and none of them answer my question. Which puts your answer in good company I suppose.


text:
What about an airfoil's shape makes air flow faster around it?
An airfoil's shape causes air above the wing to move faster than below the wing to allow for the difference in air pressure as dictated by Bernoulli's principle. This is what many sources say, but I have yet to see any explain what about the airfoil's shape or why exactly air speeds up above but doesn't below the airfoil. If I were to assume, maybe it would have something to do with the law of conservation of momentum or energy?
If you could send any sources, that would be much appreciated too!

Have you red this already?And for compressibility effects, this could also help. Please let me know if that leaves questions open.

The air on top has to travel further.

The flow of a viscous fluid can be described using the Navier-Stokes equations. This includes describing flow of air around an airfoil. Your assumption about conservation of momentum or energy is correct, both of these enter in the derivation of Navier-Stokes, together with conservation of mass:

[The Navier-Stokes Equations] describe how the velocity, pressure, temperature, and density of a moving fluid are related. [...]
The Navier-Stokes equations consists of a time-dependent continuity equation for conservation of mass, three time-dependent conservation of momentum equations and a time-dependent conservation of energy equation.

(NASA, emphasis mine)
Since there is no generic way to analytically solve Navier-Stokes, numerical approximations are typically used to derive a solution (see Computational Fluid Dynamics). When solving for the flow around a wing, the solutions show faster flow at lower pressure above the wing and slower flow at higher pressure below the wing. This might not be the simple answer you are looking for, but any answer that does not involve complex maths usually oversimplifies something.
While you are right that Bernoulli's principle relates the speed of the flow and its pressure, you have to be careful about implying causality from this:

Bernoulli-only explanations imply that a speed difference arises from causes other than a pressure difference, and that the speed difference then leads to a pressure difference by Bernoulli's principle. This implied one-way causation is a misconception. The real cause-and-effect relationship between pressure and velocity is reciprocal.

(Wikipedia)
To understand why airfoils are shaped the way they are, I recommend you have a look at the NASA page on Aerodynamic Forces. They have a good description of how the total force is generated from the pressure difference:

Thanks so much! So just to clarify, while many people say that the reason for pressure difference is Bernoulli's principle (as in velocity causes the variation in pressure), it's actually the pressure that causes the variation in velocity? Or is it a mix of both?

No, it's not like one is causing the other. Pressure and velocity are not independent, but that does not imply one is causing the other. Both pressure and velocity distribution are a result of how the air flows. And this flow can be described with Navier-Stokes (although not analytically solved).


text:
Why do some aircraft have multiple switches for the landing lights?
A question just popped into my mind: Why does an A320 overhead panel have 2 landing lights switches? What's the logic behind that? Why isn’t there only a single switch to turn on both landing lights?

It's not unique to the A320. Older 737s and 747s have 4, a 777 has 3!

On a dark morning preflight check, I can verify that the lights all work by turning each one on, one at a time, without leaving the flight deck. Less lifespan on the bulbs & less disruption to the ramp to have several quick flashes of light within a few seconds, than turning everything on, walking outside to observe everything, and then going back inside.
Plus, it's probably a hold-over from days of minimal automation (think, 727 Flight Engineer panel - now entirely replaced by automation & a few switches on the overhead panel) when each {whatever} had its own switch.
I could get creative & invent another scenario or two when I want "this" but not "that" light on, but the preflight is probably the best example of that.

You've got up votes, so this makes sense to some, but I'm not following you or seeing how this answers the question. If you can see the lights from the flight deck, would you not be able to see them if one switch turned them on instead of 2 or more switches?

@FreeMan, if I turn on 'the' switch for 'this' light & things light up, I know it - singular - is on. If one switch turns on multiple lights pointing in roughly the same place, then seeing that area light up means that at least 1 light is working, but not necessarily all of them.

Each bulb has it's own switch and the coverage area of each bulb may overlap enough not to be able to tell them apart. Got it. See, I'm not a pilot, so I don't know these things...

Some aircraft have multiple landing lights fitted to them.  Often larger aircraft have some of the landing and taxi lights attached to the landing gear and some landing lights are located in the aircraft structure behind transparent aerodynamic fairings.  This allows the crew to still make use of landing lights once the gear is retracted (the gear is usually retracted once airborne and in a continuous climb and extended at the FAF on an instrument approach).
Which reminds me of a “there I was...” story of mine.  I was flying around San Diego one overcast and cloudy night on a local IFR practicing instrument approaches into the smaller airports around KSAN (not a great idea BTW) in a Cessna 182T.  It was a busy night with multiple heavy arrivals into KSAN that evening and Miramar was busy with departures and launches as well as an emergency.  I was returning from Brown (KSDM) back to plane’s base at Montgomery (KMYF) when I got the following radio call:
“Cessna xxx, traffic 2 o’clock, three miles at 5000.  Boeing 737.  Report them in sight.”
“Cessna xxx, no joy.  I’m in IMC.”
Now you hope the controllers are professional here - it is a major airport in Class B airspace - and can keep us separated.
And it was about that time that I saw two brilliant white beams of light piercing the clouds and passed right overhead.
Well, there’s the 737.  He was not at a safe separation and pretty damned close.  If he had the gear down he might have left tire tracks over the wing of my airplane.

Safety and redundancy (is that redundant?). As a couple examples, if one of the switches breaks, you only lose that one light instead of all of them. These switches do break too, they get flipped multiple times every day and are in pretty harsh environments. Also, you could get a short circuit in one of the lights, or a light circuit.  Again, having separate switches allows you to turn off only the problem light, while keeping the rest on.

And yet Airbus replaced the switches with just a single one on all newer models (A330 upwards). I guess they don't break that often...

They may have internal logic to bypass malfunctioning circuits, guess they're banking on their switches being invulnerable.  I'd venture to guess that I've seen switches break in every type of airplane I've flown.

Most of the jets that I fly have their landing lights wired through the down locked switches on the main gear.  This means the landing light automatically turns off as the gear is raised.
It also means this is one of the ways the crew can determine if a main gear is down and locked if they have conflicting information in the cockpit.  It is easier to turn off all lights except the one landing light in question and ask tower if they see any lights than to have both landing lights on and ask the question if they see one landing light.  There is no ambiguity in the first question.  There could be in the second question.

But in a small plane (where the gear is always down), I often turn the landing light on when near airports, just for visibility.  I see commercial jets doing the same thing, turning landing lights on maybe 15-20 miles from the airport, long before the gear is lowered.

Those typically aren't landing lights but recognition lights.  They are designed to make the airplane more visible.

True, but recognition is the primary purpose of the landing light in a small plane, too.  I can certainly land at a lighted airport without the landing light - and have, a couple of times, 'cause the darned things fail quite often - but I'd be very reluctant to try a night landing without runway lights.

No, they're landing lights. At my carrier, we have the fixed  landing lights on below 18,000', day + night. The retractable landing lights are extended + on when the flaps are out. But they're all landing lights.

@RalphJ Which aircraft are you referring to?

@wbeard52   The B-737

On all the corporate jets I fly, they are called recognition lights and we land with that light on.  Most likely, boeing calls both types of lights landing lights.  It appears to me from your description the operation is the same.


text:
What inspired the unique design of the F-105 Thunderchief intakes?
The horizontally forward-swept intakes of the Republic F-105 Thunderchief is not a design emulated in other production aircraft of the time, or I think at any time.
If viewed as a more typical intake shape turned 90° it is a little less startling. What was the thinking behind this unique feature, and why was it never copied?

source

It was copied once: See the intake of the Crusader III

The inlets look like optimal Oswatitsch inlets. Pics in this post are from prof. Wittenberg's course handout on Propulsion of Aeroplanes, Dictaat D-32, TU Delft (in Dutch). Translated (by me) text explains:

Intake efficiency ${\eta}_R$ can be increased by shaping the intake body such that multiple oblique shock waves occur, followed by a normal shock wave. This has led to the idea of achieving isentropic compression via a concave shape, formed such that the compression wavelets (very weak oblique shocks) intersect each other in one point.
This type of inlet has been called the optimal (ideal) Oswatisch inlet after the researcher who during WW2 in Göttingen performed theoretical and experimental research on supersonic intakes.

So this intake design leads to optimum inlet efficiency, but poses two difficulties:

Angle ${\delta}_l$ increases with increasing Mach number, causing the inlet lip to be positioned at increasingly steeper angles and causing ever increasing external drag. Plus above $M_0$ ≃ 1.5, ${\delta}_l$ becomes larger than the angle where the oblique shock detaches at the outside of the intake, so that the design airflow cannot be realised.
The intake geometry is largely fixed, leading to possible sub-optimal conditions outside of the design conditions.

For these reasons, supersonic intakes with variable geometry and partial isentropic compression were designed, and used in subsequent supersonic aeroplanes. As shown in the pic above. The normal shock wave is the only source of loss in this set-up.
------Updates-------
@PeterKämpf linked two pics in a comment, showing some more details of the F-105 intakes:

An adjustable strip can be seen in the last photo, providing some adaptability in intake characteristics.
A further link provided by @mins to this NACA document, where several inlet configurations are measured. The drawing above is from the report, which discusses several intake configurations researched pre-production and it does not provide any statements on variability of the geometry. From the abstract:

A 1:13-scale Republic F-105 wing-root inlet configuration in which inlet components were varied was tested...Inlet performance and engine-face flow distortions as affected by pitch, sideslip, inlet lip sweep, contraction ratio, boundary-layer control, and engine bypass are presented and discussed.

The F-105 did have a variable-geometry intake: There was an adjustable ramp inside the intake duct.

See also NACA-RM-SL7A28: Wind-Tunnel Investigation of the Republic F-105 Inlet with Various Modifications at Mach 1.41, 1.81, and 2.01, from which previous diagram is extracted.


text:
COM Transceiver problem and SWR test
I have a VHF COM problem. I have a new composite structure aircraft (a Berkut) with an older VHF transceiver, (a Bendix King KX-155 TSO), that has significantly reduced range in certain situations. The VHF antenna is in one of the two winglets, and, obviously, does not have ground plane attached to it. The symptoms are somewhat bizarre.
I am based at Prescott's Love field, and most of the time we depart on runway 21, where the approach end of the runway is at the north end of the field, which is only about 6,000 feet from the control tower. When I taxi out to the quick check area prior to takeoff, the radio works fine both transmit and receive, until I am about 4-5000 feet away from the tower. After that, for a few feet further away, I can hear the tower, but they can no longer hear me. When I get to the end of the taxiway (run-up area) I can no longer hear the tower at all. When I taxi back (closer to the tower), both transmitter and receiver begin working again.
Once I am airborne, the transmitter and receiver both work satisfactorily within 20-25 nm from the field but start to degrade as I move further away. On cross-country flights, where I attempt to maintain communications with ARTCC (for flight following), the transceiver routinely fails at longer ranges before I have reached the transition point where the current sector controller would normally transfer me to the next controller.
I went to the local Avionics shop to get some expert help. The tech there performed an SWR test on my aircraft, and a bench test on the radio. Both were normal. They happened to have an identical model KX-155 they had removed from another aircraft sitting on a shelf, that they let me borrow. I replaced my unit with theirs and experienced virtually identical symptoms. That does not of course indicate that the problem is NOT in the unit itself. (both units could have similar faults in them), but it is not likely.
The normal SWR test raises my first question. Does the SWR test only send the RF pulse down the core of the coaxial cable? i.e., if there was a break, or crimp or other failure in the shielding, would the RF reflection from the SWR test also show an issue from that? and secondly, (because another avionics tech suggested this to me) can a failure/degraded, crimped or corroded) shielding on the RG-58 coax cable cause an issue like this? And if so, is there another test I can perform on the aircraft to definitively diagnose this issue?
I need to diagnose this as I am planning on a complete avionics suite upgrade (to the Dynon HDX suite), including their HF transceiver and COM control panel, and I don't want to install that complete system if the issue is actually in the coaxial cables or the antenna until I have fixed this.

The radio I have installed is a Bendix King KX155, and it has three coax connectors in the mounting tray, one for VHF COM (transmit and receive), one for VOR (receive), and one for ILS Glide Slope (receive). Today I started trying to attach an SWR meter directly to the VHF COM coax, (one of 8 or 9 RG-58 cables), to eliminate issues in the mounting tray connectors).  In tracing the cable, to make this connection, I discovered that it is not connected to the VHF COM antenna at all, it is connected to the VOR/ILS antenna.

First, let me try to clarify some of the theory and terminology.
The coax cable is an unbalanced system. That is (in theory) all the energy is carried on the conductor and nothing on the shield. With the standard antenna, the conductor is connected to the antenna element and the shield to the ground plane. Without the shield, the energy can be radiated outward with the ground plane shaping the pattern.
The length of the antenna element is typically a 1/4 wavelength of the frequency in the center of the operating frequency band. The 1/4 wavelength will maximize the radiated energy. If the antenna was "perfect" and you were on the design frequency, the VSWR would be 1:1. At the top and bottom of the band, VSWR is typically 1.2:1 or 1.3:1. Any flaw in the cable or the antenna will cause the VSWR to increase. It's a measure of reflected energy which occurs when there is an impedance mismatch. A flawed ground plane won't have a material impact on VSWR unless it is close enough to the antenna element to act as a partial shield.
But I don't know what kind of antenna you have. Many composite aircraft use a dipole antenna embedded under the skin to compensate for the lack of a ground plane. The dipole antenna looks like the "T"-shaped antenna that sometimes comes with FM radio receivers. The difference is in the aircraft with vertically polarized AM signals, it is turned sideways so the top of the "T" is vertical.
The dipole doesn't need a ground plane as it is a balanced system. In a balanced system, the energy is balanced across both conductors (no shield.) With a dipole antenna, you have to convert the unbalanced signal on the coax to a balanced signal before the antenna. This is done with a balun (a BALunced to UNbalanced converter.)
If you have a dipole antenna, the VSWR will be a good measure up to the balun. If there's an issue with the dipole past the balun, it may not be detected by the VSWR test. The best way to detect an issue is examination of the antenna (which is often difficult when it's bonded to the skin.)
One option that may or may not help is to test with an FFT based cable analyzer. With them, you can see any mismatches and they can tell you how far down the cable the issue is located.
Your other choice is to replace the antenna if practical.

The antenna is a dipole, as you describe, with the coax connected in the middle. I'm not sure about the balun. Your post is the first I've heard of this. I will look at plans to see if it's in there. Do received signals then get converted to unbalanced to travel along the coax back to receiver?

Yes. The balun is bidirectional.  It's also a passive device. Just Google it. You'll get lots of information. Just remember they are impedance specific. You want 50 ohms. I suspect the lack of a balun is 'unbalancing' your coax. That causes energy to be radiated by the coax shield which is messing with your radiation pattern.

Could be, but there is a BNC connector between the wing and the wing strake, where the wing is attached to the fuselage, and the aircraft was warehoused for a significant period of time, in pieces, where that connector would have been disconnected and exposed. I doubt the balun is missing, since if the balun was missing this problem would have surfaced before it was disassembled and put in storage.  So my first line of investigation is into the connectors, I plan on first putting an SWR meter on the outboard (wing) side of that BNC connector, to test system from that point out to the antenna.

When I googled baluns, the Wikipedia article seemed to indicate that the balun is only required if using coax with a different impedance than the antenna impedance. Also, one line in the text struck me... it said "without a balun, the shield of the coax could couple with one side of the dipole, inducing common mode current, and becoming part of the antenna and unintentionally radiating." My antenna is wired in exactly that way.

I suspect what the Wikipedia article describes is what's happening. It's hard to guess how much coupling is occurring, but any significant radiation from the coax shield will distort the radiation pattern away from the omni pattern of the dipole. I'm conservative and would use a balun with a dipole. In my experience with radios, the two biggest issues long term are antenna impedance issues (bad connections, broken shields, poor placement) and grounding and bonding problems. The first hurts Tx/Rx range, the second causes noise.

"all the energy is carried on the conductor and nothing on the shield": A coax is a 3-conductor line in HF: Current in shield inner side and center conductor are opposite like in a balanced line. True, there is no current on the outer side of the shield. Incorrectly  unbalanced/balanced antennas with a nonzero potential at feed point create a common-mode current in the outer side of the shield, the shield radiates, the radiation pattern is changed. This happens independently of VSWR. More.

It is common for an unbalanced monopole antenna on a coax feed line without a ground plane to exhibit weird radiation patterns & behavior like this. Walkie-talkies use monopoles but their feedlines are vanishingly short so they escape these effects. In a metal airplane, the coax shield is connected to the fuselage skin to form a ground plane or counterpoise and the antenna behavior is thereby tamed and made predictable.
The usual way to furnish a fuselage-mounted monopole with a counterpoise in a nonmetallic plane is to glue a square of copper sheeting to the inside of the skin and mount the antenna in the center of the square, with the coax shield connected to the copper.
You can also glue long strips of copper tape in a radial pattern extending outward from the antenna mount to accomplish the same effect.
In either case, the dimensions of the copper sheet or the lengths of the copper radials need to be adjusted to get the best electrical match between the feed line and the antenna, which will suppress radiation from the feedline shield. This is called pruning and shortwave enthusiasts who make their own monopole antennas have to do this.
Suppressing radiation from the feedline is important because it is accompanied by high voltages on the shield and significant amounts of radiation inside the fuselage. you can get bad shocks and RF burns if you touch the shield, and the radiated energy will seriously disrupt other electronic devices in the cockpit. Baluns are commonly used by ham radio guys to block "RF in the shack" but their design and use is something of an art.


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Why don’t most aircraft have emergency braking parachutes?
Braking parachutes were standard on first-generation jetliners, but have since fallen almost entirely out of use except on military aircraft; essentially the only civilian aircraft nowadays to still carry braking parachutes are some Learjets, which have emergency parachutes to help prevent an overrun during a landing or high-speed rejected takeoff if the runway is slippery or if one of the aircraft’s primary braking systems (reversers, spoilers, wheelbrakes) malfunctions.
Given the relatively frequent occurrence of runway overruns (often resulting from slippery runways or from takeoffs rejected near or after V-1), why aren’t most civilian aircraft (especially large, heavy ones, which need lots of runway to slow down even under ideal circumstances, and need all the help they can get if circumstances are less than ideal) equipped with emergency braking parachutes to help prevent overruns?

Because EMAS is a lot more effective... How do you quantify that overruns are frequent? Doing an NTSB search for Part 121 operations with the word "overrun" gives 27 results dating back to 1983, only one of which had a fatality (to a child in a car the aircraft hit). I'm sure there are more with different search terms (over run, etc), but I don't think it's statistically significant. Plus by the time an aircraft reaches the end of the runway where the chute would be deployed, the speed is too low for it to be effective.

Possible duplicate of Do any commercial airline models have a parachute at rear to help in landings? Maybe not the same exact question but the answer covers it.

@Dave: That question asks if any commercial planes do, and that answer says why they don't use parachutes for routine landings.  This question asks why they don't have them in case of emergency.

@Sean many of the reasons transfer over. Breaks and thrust reversers are used in both regular and emergency landings. As noted by Ron EMAS also has a lot to do with it as well. I takes more than me to get it closed so if others dont feel its a dupe it wont get closed.


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Rules upon accessing the aircraft after emergency landing
The question is inspired by the recent emergency landing of Ural Airlines Flight 1383. Please correct me if it belongs to Aviation.SE or other site.
An aircraft performs an emergency landing somewhere in the field. The vessel safely lands, no one is injured. AFAIK even in this case everyone is immediately evacuated from the board without their personal items (and likely without shoes not to damage the ramp) since the aircraft may have hidden damages that may lead to fire or something.
Suppose some passenger is perfectly fine with being delivered to the middle of nowhere and wants to get his backpack from the cabin and go away. Can he get the access to the aircraft after evacuation? What is the procedure of regaining personal items?
Some other hypothetical circumstances:

the passenger needs not a backpack from the cabin but a bag from the luggage compartment;
the passenger  needs insulin or other medicine from the backpack;
there is a dog in the cage in the luggage compartment which should be let out.

Will any of these or other circumstances affect the decision?

Seems like a legal question to me. They tell you to stay away from the aircraft (as they surely will) and you decide to disobey? They like to claim that it's illegal not to follow crew members' instructions (presumably their interpretation of 14 CFR 125.328 Prohibition on Crew Interference). The actual situation seems a bit murky, maybe the violent removal of Dr. Dao from a United aircraft is a precedent.


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What happens when the runway is unusable at an isolated aerodrome?
What happens when you fly to isolated aerodrome in turbine engine aircraft without predetermined point procedure and just upon arrival for example an aircraft crashes on the runway and you can not land, you have fuel for 2h of flying due to fuel reg when flying to isolated destination aerodrome and what happens next? Is there an requirement for isolated aerodrome to have maybe 2 separated runways? Or something else...

It doesn't need to be an isolated aerodrome.  In 2022, Singapore Airlines flight SQ-319 waited for the weather to improve rather than diverting, when there was no improvement they flew to the alternate but the weather had closed in there.  They messed up the first approach, finally managed to get down and ran out of fuel while taxying to the stand. https://www.avherald.com/h?article=50f11fc3

How sure are you that all those details matter? Why not just 'you cannot land, you have fuel for 2h…'?
How could there be a requirement for any 'drome to have more than one runway…?

The Gimli Glilder had no fuel and only a closed airport with people on the runway.  At least they had a runway.

Does this answer your question? May an emergency aircraft land on a closed runway?

In the scenario where a large passenger jet is in a situation where its only landing option is closed with insufficient fuel to get to another landing strip then the options are limited to attempting to land at the closed airfield, or finding a place for an emergency landing, and neither option is likely to end well.
Airports are not required to have multiple landing strips, even isolated ones.  The most isolated airport in the world is probably Mataveri International on Easter Island, in the Pacific. The closest airport is in Chile, 2400 miles away. It has a single 10,000ft strip.
The key to safety is to not get into that situation in the first place. In the case of Mataveri, only one flight is allowed to fly to it at once, that flight must land successfully before another is allowed to depart to it, and flights must carry a lot of extra fuel.

Wow, so I wonder how that airport is staffed. You can literally be home until someone schedules a flight and then you head to the airport while the plane is in the air.

With Mataveri, if memory serves, there's also a weather decision point near the route's halfway point. If the weather seems too rough to land in, the pilots turn around and go back to SCL.

The Gimli Glider is a perfect example of this situation. No fuel and only an old closed runway or making a dent in the ground.

It's pretty simple. You have 2 hours of fuel on board, the nearest useable strip is over 2 hours away, and there is a wrecked airplane on the runway that you'd confirmed was useable before you left, or maybe a moose that just walked across and died of a heart attack in the middle 5 minutes before you arrived.
Normally on trips to remote locations, you have enough fuel for the round trip and just head back (assuming you weren't compelled to land anyway to help injured people). But the company may have a fuel cache at a location so that more payload can be flown out, so that kind of situation is possible.
What are you going to do? The choice is land on a much shortened surface, or on a patch of open ground somewhere, or crash into the trees.
Since a skilled pilot won't need the entire runway, in the absence of other options they'll just land anyway, over, or short of, whatever is obstructing the runway, depending on where it is. You work around it. You may be stuck there until the obstruction is removed, but that's the bush flying life and you include those ramifications in your decision.
If you arrived and the runway was flooded with a foot of water, and you never checked, and didn't include return fuel for the trip, that's on you for your poor planning and maybe you aren't cut out for bush flying, which is very much a live-by-your-wits pastime.

Lets say im flying B747

On floats that is.

Then you'd probably be on your way to killing a couple hundred people, @FilipAdam. Bad decision making. However, any airport capable of landing a 747 will, most likely, have a taxiway that could be used in an emergency.

@FilipAdam You'll be on an IFR flight plan and will divert to your alternate same as if the weather was below minimums or the airport was closed due to a terrorist attack or something.  IFR fuel requirements are trip>approach>missed approach>fly to flight planned alternate>approach>land>30 minutes fuel remaining on landing. What you're describing would only apply to a VFR bush operation on wheels. My bush experience is on floats, where runways don't even come into it and I was always flying with round trip fuel.

@JohnK That's not correct, you can fly IFR without an alternate (see e.g. this answer). The whole point of the question was that the destination is isolated, which means there is no viable alternate available.

@Bianfable Technically yes, but NAIFR (in Canada anyway) requires VFR conditions forecast at destination so unless the isolated location the 747 is heading to has a TAF available, it won't be going NAIFR.

If you flew to an airfield without having a viable plan for an alternate destination in the event that you couldn't land there, then that's your mistake as the pilot. It's true that the law does not require you to declare an alternate on your flight plan, but any sensible pilot should have a plan for what to do in the event that they couldn't land.
There are plenty of reasons why you might not be able to land, mostly weather-related and much more likely than an unexpected aircraft crash. You need to be prepared for them. @JohnK gives you a good summary of the options open to you if you do find yourself in that position.

The question is about an isolated aerodrome, where ICAO specifically doesn't require an alternate (see this answer): "the aerodrome of intended landing is isolated and there is no suitable destination alternate aerodrome."

The fact that the law does not require you to officially declare an alternate in your flight plan does not excuse a pilot from having a plan in the case that they are unable to land there. The plan does not have to be a legally acceptable "alternate", but some way of getting the plane on the ground with a good chance of not killing the occupants.

Or something else...

You have several pre-scouted ditching/off-field landing locations, ideally already keyed into the FMS, briefed, etc. If you were in the business of flying 747s to an "off-field/ditching is the nearest alternate" location, you'd be better be prepared, have seen the locations in person, or at least on recent satellite or aerial imagery, have consulted with local people/authorities, talked to anyone else who flies/flied to that destination that you can find, etc.
Just as if you were driving your car into wilderness where if the car failed you could die of exposure if unprepared. You have to be prepared, have a plan, have it briefed, and not have too worry about it when you're enroute. If you make that flight, you are accepting that the off-field ditching is an alternative and an acceptable risk. Otherwise you don't fly. Simple as that.
The aerodrome has no obligation to you. If it's closed/unavailable and you have no other options, it your mess to deal with, so you have to be prepared.

Lets say I'm flying B747

You're flying it without passengers, on a ferry flight, mind you, just to be clear.


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What is the rationale of a weight/passenger value for the ICAO TCAS requirement?
What is the rationale for the figures 5,700 Kg and 19 passengers?
Excerpt from TCAS's Wikipedia entry page:

It is a type of airborne collision avoidance system mandated by the
  International Civil Aviation Organization to be fitted to all aircraft
  with a maximum take-off mass (MTOM) of over 5,700 kg (12,600 lb) or
  authorized to carry more than 19 passengers.

I would guess costs-benefits tradeoff

Can you expand please?

The specific numbers were probably chosen with a representative list of aircraft in mind. The lawmakers may have done a cost/benefit analysis on several planes, and decided which ones it made sense for. Then a number that included and excluded the appropriate planes was chosen. This is heavy speculation on my part though.

The numbers aren't random, though at first glance the rationale may not be obvious.
Weight
5700 kilograms is (roughly) 12,500 pounds - This aligns with the FAA definition of a "large aircraft" (an aircraft with a maximum certificated takeoff weight of more than 12,500 pounds).
Large aircraft tend to be "working airplanes" in passenger or cargo service, and will be operating to/from busy terminals. They will therefore benefit substantially from TCAS, and the operators can theoretically afford to equip their fleets.
Seating Capacity
Carrying more than 19 passengers further includes aircraft which may not be "large aircraft" but might be used as "working airplanes" in regular airline/commuter service carrying passengers (and would therefore benefit from TCAS, and theoretically be producing revenue to offset the cost of equipping them).
This roughly aligns with FAR 121.391 flight attendant requirements (Even relatively small aircraft - maximum payload of 7,500 pounds or less - are required to have a flight attendant on board to assist in evacuation in the event of an emergency, so it logically follows that such aircraft should be equipped with TCAS to avoid at least one possible type of emergency (mid-air collision).

As Federico pointed out, this is largely a cost/benefit trade off (nobody would argue for a flight attendant on a Cessna 150, similarly the TCAS safety features would be overkill for most Cessna 150s in the world).

I wonder if the smallish jets (Citation, LJ 45, etc) might not benefit? Anyone know the general costs associated with TCAS?

@CGCampbell they probably could - nothing stopping people from installing a TCAS system in them except money ($20,000 for the box, plus install - as of right now)

@CGCampbell Most Learjets and Citations have TCAS, although it is only required for turbine powered aircraft with 10 or more seats operating under 14 CFR 135.

Basically, they require it on aircraft that will in normal situations be used in airliner operations. There's nothing prohibiting it from being installed in any aircraft, as long as they want to pay for the electronics, and/or certification costs if the part has never been fitted to the type in question. Also, as a note there are a significant number of business jets that are large enough to be in the 5700kg weight range.

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How does having multiple ATC towers affect airport operations?
I know there are airports with more than one ATC Tower, though I only know it from my own country (SCHIPHOL - EHAM). This airport has two towers called Tower-Center and Tower-West. Tower-West is built because of a sixth runway (18R - 36L), that wasn't clearly visible from Tower-Center. (They found this out after completion of the sixth runway.)
How common is it an airport decides to built a second tower, and are there a certain rules or limitations before the decision can be made?
Next to that; what are the practical consequences for pilots and ATC's? Do they not only switch between startup- and ground-controllers but also between several ground controllers?

At larger airports it is fairly common to have more than one tower, but it all comes down to how well the tower controllers can see airplanes.  Sometimes they have different towers for ground control frequencies and tower control frequencies, and the position of the tower is optimized for the appropriate task.  For very large airports, they may need towers in different areas of the airport to properly see airplanes at each runway.
As far as practical consequences it doesn't matter much whether they have one or more towers.  At very busy airports they split up the tower/ground controllers/frequencies because one person can only control so many airplanes at a time.  For instance, there may be one controller for the North runway and one for the South runway.  In this case, there could be only one ground controller, or there may be two or even more, depending on the complexity of the ground operations.  With multiple ground frequencies, if you need to taxi from one controlled area to another, the controller that you are talking to will tell you to hold short of a particular point and contact ground on the other frequency.  Once you contact the second controller, they will clear you to continue taxiing.
In short, it is very specific to the local conditions, and they do what they have to in order to properly control the traffic.

How common is it an airport decides to built a second tower, and are there a certain rules or limitations before the decision can be made?

It's fairly common where there's more than one runway, and it has a lot to do with visibility from the ATC Tower cab. Under optimal conditions, ATC would need to be able to see all airfield paved areas with a minimum Line of Sight angle which varies from regulator to regulator.
This can sometimes prove difficult for runway thresholds if their elevation and distance to the tower location make this angle too low. Big terminal buildings (or any other building for that matter) can also be an obstacle to visibility, especially on apron areas.
The decision to go for more than one tower, from an operational point of view, comes down basically to the need to have control of all airfield areas. Building an additional control tower is not only very costly, but also adds complexity to ground operations which is always an undesirable (albeit inevitable) effect. In some airports apron control is transferred not to another tower, but to follow me personnel under the supervision of ATC, for example.
As for the practical consequences for pilots and ATC, Lnafziger has done a better job answering your question than I could have hoped to achieve.

These days building more than one ATC tower in an airport is not advisable because of availability of many technological tools that help you to extend your surveillances over the far corner of the airport and prevent runway incursion. This is called A-SMGCS (Advanced-Surface Movement Guidance and Control System) depending on the need of airports there are 4 levels using radar and modern surveillance plus data links techniques for making visible aircraft and vehicles,  I believe that is cheaper and less complex than making a new tower which in its turn would be an obstacle for flight operation.

You cannot rely on A-SMGCS for all tower tasks. Obstacles on runways, such as wildlife, birds, vehicles [without transponder], or even persons will not show up. You also cannot provide visual separation if you cannot see the runway, meaning that capacity would potentially be reduced. In short, a tower controller needs to be able to [visually] see the runway they is working with.

While I like your comment; but in rare occasions and because of lack in airport layout or miss calculation of tower location or poor visibility with long duration, and…. the situation may suggest additional ATC towers.  As I mentioned there are 4 levels of A-SMGCS with different capability and sensors can give you required possibility. Take into account remote tower technology which meet many ATC tower requirements and prevent runway incursions, it may suggest a business case and cost benefit study for the optimum salutations.

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